Optical crown glasses



Aug. 13, 1963 H. BRESMER ETAL 3,100,714

OPTICAL CROWN GLASSES Filed Oct. 3, 1961 I I I I I I Q" 10 2a a0 41; 56 60 76 80 90 8/0 INVENTORS B) W M ZWM 3,160,714 OPTICAL CROWN GLASSES Heinz Briimer and Norbert Meinert, Wetzlar (Lahn), Germany, assignors to Ernst Leitz, G.rn.b.H., Wetzlar (Lahn), Germany Filed Oct. 3, 1951, Ser. No. 142,551 Claims priority, application Germany Nov. 5, 1960 7 Claims. (Cl. 106-54) Our invention relates to optical glasses which lie in the range of strong to strongest crown glasses.

Recently the application of lanthanum crown glasses for objectives of high value has attained increasing importance, yet in the preparation of normal objectives recently, as formerly, strong and strongest crown glasses have been used predominantly. These two types of glasses were, until the present time, melted down on a silicate base with partial substitution of boric oxide and very high proportions of alkaline earth metals, principally barium oxide. The majority of these glasses is strongly sensitive to spotting and, in fabrication, produce a high quota of rejects.

Most recently the tendency is to use phosphoric oxide as a base glass with the addition of boric oxide. The glasses thus melted down are essentially resistant to chemical attack and spotting but have the disadvantage that they incline very easily in commercial production to crystallization. In some types the production of pressings and gob by this means is not possible.

By means of systematic stabilizing reasearch it has been found that all of these obstacles can be obviated if one selects as a glass base a ternary combination consisting of silica, bon'c oxide and phosphoric oxide. In this formation of a glass base one uses, besides other oxides, larger amounts of oxides of the alkaline earth metals with the exception of beryllium and radium and obtains glasses which are essentially more stable than the original silicate glasses and which do not exhibit the tendency to crystallation of the phosphate glasses.

The glasses of the above invention have as a glass forming base a combination of silica, boric oxide and phosphoric oxide within the following limits:

Percent by weight SiO 5.5 to 20.0 B 10.0 to 31.5 P 0 10.0 to 16.0

At the same time the sum of the three ingredients is to be between 35 and 47% by weight of the finished glass.

In the accompanying diagram the claimed field of the ternary combination, SiO B O --P O extended to 100% by Weight of these three ingredients is shown. The corner points of the hatched field have the following values.

(1) SiO =11.7 B O =54.3 P 0 2340 (2) SiO =11.7 B O =67.0 P O =21.3

States Patent 3,100,714 Patented Aug. 13, 1963 ice alkaline earth oxides can be substituted partially within the given limits by the following oxides, whereby, however, the given limits for the calciumand barium-oxide portions remain constant:

The sum of the substitute oxides can amount to 32.5% by weight.

It is appropriate to add the phosphoric oxide entirely or at least in part in the form of boron phosphate, meta, pyroand ortho-phosphates of the alkaline earths as well as of zinc and/ or cadmium.

In Table 1 are examples of compositions of strong crown glasses according to the invention in percent by weight.

Table 1 Melt No A/Br 1 A/Br 8 GIN/A9 GIN/Br 1 10. 0 10. 0 11.2 10. O 15. 0 17. 0 17.0 15.1 15. 0 15.0 16.8 14. 9 10. 0 3.0 10. 9 l8. 9 12.9 9. 2 27. 5 23. 5 27. 5 29. 5 10. 0 4. 0 4. 6 13. 7 7. 0 7.0 5. 0 4. 6 4. 6 4. 6 l. 6352 1. 6291 1.6 "8 1.6408 55.4 56. 6 58. 7 54. 8

Melt No GIN/A11 O/N/AIZ C/N/A13 Melt No GIN/Br 2 A/Br 17 3/131 4 B/Br 14 Melt No E/Br 10 E/Br 11 In Table 2 are shown two examples in which the phosphoric oxide is substituted as metaphosphate.

T able 2 MeltNo I A/Br12 l A/Br13 1400" C. The melt is stirred as in the usual manner for homogenizing.

The pouring temperature can be so chosen that the necessary viscosity for the particular casting method has been reached. It can be cast equally well according to the old method or according to modern belt casting methods. The transformation zone of the glasses lies, al-

10.0 120 Ways according to the composition, between about 550 22.0 19.1 5 13.0 13.9 and 600 5 10 10 The following Table 4 shows the chemical stability of &3 each of two glasses of the same optical position. In it $3 are A1 and A2 usual glasses of comerce while B1 and B2 6298 6344 are glasses according to the above invention. The tests 56- 5 4 were carried through according to H. Bredow, Glas-Email- Keramo-Technik (1959), vol. 8, pages 297-299.

Table 4 I A1 131(0/N/A5) I A2 B2 (E/Br10) 551.6413. m=1.64l4. n..=1.6229. m=1.6220. v.=55.24 6.:5435. v..'=60.1 v.=60 0 11/10 HNOs, 329.0 mg. Standard acetate, 254.0 mg. SiOz, 30.0% by weight. 13203, 15.0% ,by weight.

11/10 HNOz, 104 mg.

Standard acetate, 114.0. S101, 10.0% by weight. B201, 15.1% by weight.

BaO, 48.0% by weight. BPO 14.9% by weight. NazO 0210, 9.2% by Weight. A1 O 13:10, 27.5% by weight. 7.0% by weight. ZnO, 13.7% by weight. ZnO A1 0 5.0% by Weight. I T10 ZrO;, 4.6% by weight.

n/10 HNOz, 100 mg. Standard acetate, 74 mg. $10,, 12.0% by weight. B101, 17.7% by weight.

BPO4, 14.9% by weight.

OaO, 4.6% by welght. 13610, 36.2% by weight. SrO, 7.1% by weight. ZnO, 6.0% by weight. A1201, 2.5% by ewight.

11/10 HNOa, 397 mg. Standard acetate, 203.0 mg. S104, 30.0% by weight. 13:03, 18.8% by weight.

2 1% 2.0% by weight.

13:10, 47.6% by weight. A1201, 1.6% by weight.

Table 3 contains a collocation of melts whose optical values lie in the region of the strongest crown glasses.

Table 3 Melt N0 GIN/A7 A/Br 14 11/131 15 A/Br 16 D/Br 5 D/Br 7 D/Br 3 V For the melting down of colorless optical glasses according to the invention raw materials of high purity grade are intimately mixed and the mix is melted in a crucible. According to the invention there can be added to the glasses in the customary manner small portions for decolorizer, for example, arsenic oxide or antimony oxide.

Platinum is to be used as a crucible material although crucibles of otherwise usable materials can also be used.

The melting temperature lies between 1300 C. and

Having described our invention, we claim:

1. Optical glass having an index of refraction 71 above 1.61 and an Abbe number v above 48.2 and consisting essentially of, (1) 35 to 47 percent by weight of silica, boric oxide and phosphoric oxide of which the silica content lies between 5.5 and 20 percent by weight, the boric oxide between 10.0 and 31.5 percent by weight and the phosphoric oxide between 10 and 16 percent by weight and (2) the balance of 65 to 53 percent consists essentially of oxides selected from the group consisting of magnesium oxide, calcium oxide, strontium oxide and barium oxide of which balance calcium oxide is present in amount equal to at least 5 percent by weight of the glass composition and barium oxide is present in amount equal to at least 20 percent by weight of the glass composition.

'2. Optical glass according to claim 1 in which the oxide (2) is substituted up to an amount of 32.5 percent by weight by the following oxides within the above stated limits: 1

Percent by weight ZnO and/or CdO 0 to 15.0 A1 0 0 to 10.0 La O to ZrO 0 to 16.0 PbO 0 to 7.5 T10 0 to 7.5 T3205 and/Or Nb205 0 to 7.5 W0 0 to 7.5

3. Optical glass according to claim 1 in which the phosphoric oxide is introduced into the composition at least in part in the form of boron phosphate.

4. Optical glass according to claim 1 in which the phosphoric oxide is introduced into the composition at least in part in the form of a phosphate of an alkaline earth metal. 7

5. Optical glass according to claim 2 in which the phosphoric oxide is introduced into'the composition at least in part in the form of a phosphate of zinc.

6. Optical glass according to claim 2 in which the References Cited in the file of this patent phosphoric oxide is introduced into the composition at UNITED STATES PATENTS least in part in the form of a phosphate of cadmium.

7. Optical glass according to claim 1 in which an oxide 2,532,386 'Armlstead 1950 of the group consisting of arsenic oxide and antimony 2,615,817 stanworth 1952' oxide is introduced into the composition. 5 $009,819 Geficken et a1 21, 1961 

1. OPTICAL GLASS HAVING AN INDEX OF REFRACTION NE ABOVE 1.61 AND AN ABBE NUMBER VE ABOVE 48.2 AND CONSISTING ESSENTIALLY OF, (1) 35 TO 47 PERCENT BY WEIGHT OF SILICA, BORIC OXIDE AND PHOSPHORIC OXIDE OF WHICH THE SILICA CONTENT LIES BETWEEN 5.5 AND 20 PERCENT BY WEIGHT, THE BORIC OXIDE BETWEEN 10.0 AND 31.5 PERCENT BY WEIGHT AND THE PHOSPHORIC OXIDE BETWEEN 10 AND 16 PERCENT BY WEIGHT AND (2) THE BALANCE OF 65 TO 53 PERCENT CONSISTS ESSENTIALLY OF OXIDES SELECTED FROM THE GROUP CONSISTING OF MAGNESIUM OXIDE, CALCIUM OXIDE, STRONTIUM OXIDE AND BARIUM OXIDE OF WHICH BALANCE CALCIUM OXIDE IS PRESENT IN AMOUNT EQUAL TO AT LEAST 5 PERCENT BY WEIGHT OF THE GLASS COMPOSITION AND BARIUM OXIDE IS PRESENT IN AMOUNT EQUAL TO AT LEAST 20 PERCENT BY WEIGHT OF THE GLASS COMPOSITION. 